Means for determining the shear strength of earth in situ

ABSTRACT

Apparatus and a technique for the in situ measurement of the torsional shear strength of remotely located soil is provided. A probe and a reaction in close proximity to each other are embedded in soil in place at a remote point, e.g., the end of a bore hole; torque is applied to the probe, and resistance to rotation of the probe in the soil relative the reaction anchored to the soil is sensed and transmitted electrically to the surface as useful data. The apparatus is installed very remote from an operator&#39;&#39;s station by cooperatively employing drilling casing or drilling equipment by which the bore hole is maintained or formed.

United States Patent 1191 Wilson et al.

1 1 Jan. 9, 1973 [76] Inventors: Stanley D. Wilson, 3668 Albion Place North, Seattle, Wash. 98103;-

Richard K. Harris, 7321 48th Ave. N.E., Seattle, Wash. 98115 [22] Filed:

July 2,1970

[21] Appl. No.: 51,997

[52] US. (:1 ..,73/101, 73/84, 73/88 E [51] lnt.-Cl. ..G01n 3/24 [58] Field ofSearch ..73/l0l,88 E, 151,84;

[56] References Cited UNITED STATES PATENTS 3,175,392 3/1965 Tharalson et a1 ..73/84 2,141,030 12/1938 2,108,174 2/1938 2,050,970 8/1936 2,603,967 7/1952 3,552,195 1/1971 Koprowski ..7 3/l0l 3,216,243 11/1965 Ber'gfeltetalnu ..73/l0l 2,993,367 7/1961 Fletcheretal.... ..73/101 5/1955 L68 .73/101 Primary Examiner-James .I. Gill Assistant ExaminerMarvin Smolla'r Att0rney.Ford E. Smith 1 ABSTRACT Apparatus and a technique for the in situ measurement of the torsional shear strength of remotely stalled very remote from an operators station bycooperatively employing drilling casing or drilling equipment by which the bore hole is maintained or formed.

3 Claims, 6 Drawing Figures MEANS FOR DETERMINING THE SHEAR STRENGTH OF EARTH IN SITU SUMMARY OF THE INVENTION It is known to determine the torsional shear strength of soil in situ by the use of a vaned probe, adapted to be embedded in a soil specimen at or closely adjacent the earth surface, to which torque is applied. The application of torque on the vaned probe tends to cause a cylindrical body of soil to be sheared from the surrounding body. Resistance between the two bodies to the shearing force constitutes data useful to soil engineers and geologists in their investigations respecting the condition of the earth. Such operations are disclosed in various technical publications, such as No. 193 (1957) of the American Society for Testing Materials entitled Vane Shear Testing of Soils, and in prior patents. Vaned probes are shown in Carlson, U.S. Pat. No. 2,603,967, Gibbs, U.S. Pat. No. 2,907,204, Fletcher et al, U.S. Pat. No. 2,993,367, Bergfeldt, U.S. Pat. No. 3,216,243, and applicant's prior patent, U.S. Pat. No. 3,364,734, together with discourses on their use in soil testing. In situ testing where the situs of the soil is extremely remote, for example, hundreds or more of feet in the earth or underwatcr as often occurs in oil exploration activity presents practical problems.

The problem of placement of the testing equipment in the earth and of establishing a base of reference proximate the test site is considerable. The apparatus of this invention comprises a varied shear probe mounted in the leading end of an extending hollow casing, and associated with closely located torque producing means fixedly mounted in the same casing. The leading end of the casing has anchor means engageable in the earth proximate to said probe. A sensor between said casing and its anchor means and the shaft of the vaned probe senses resistance to shear of the probe when torque is applied. An electrical signal is developed in the sensor which is easily transmitted to without the bore hole. At the surface, such signals are measured and provide the useful data. The casing is adapted to be raised and lowered on a cable within a drill casing in the hole. Placement of the probe is facilitated by providing extensible retractible pawls in the instrument casing which when'extended may be engaged by the drill casing to apply downwardly directed mechanical force to drive the probe and reaction means into the soil. A technique of employing the equipment is disclosed. It will be seen that the main object of the invention is the provision of a method and means for accurately and simply measuring the shear strength of undisturbed soil axially ahead of a bore hole and remotely located from an operator's site.

DESCRIPTION OF THE DRAWINGS:

FIG. 1 is an elevational view mostly in section showing a preferred example of apparatus embodying this invention;

FIG. 2 is an enlarged view in elevation of the shear testing probe and cooperable reaction employed at the head end of the apparatus;

FIG. 3 is an enlarged elevation view showing the torque-generating and resistance sensing section of the apparatus;

FIG. 4 is an enlarged elevation view of the apparatus section containing extendible means by which the apparatus may engage and drive into soil in place; I FIG. 5 shows in enlarged scale the details of said extendible means; and

FIG. 6 is a cross-section view on line 6-6 of FIG. 2.

DESCRIPTION OF THE INVENTION:

The probe 10 comprises shank or shaft 12 having vanes 14 radially disposed on its front end. The leading edges 16 of the vanes are chamferred as shown to ease their entry into the earth. Other forms of probes will readily come to mind.

Reaction 'head 20 comprises annular body 22 having forward extending conical body 24, provided with a plurality'of radial vanes 26. Body 22 at the rear is internally threaded to couple with threaded boss 27 of con- I nector collar 28 as shown in FIG. 3. Conical body 24 has a longitudinal passage 25-which receives shaft 12 and provides bearing support of probe 10,. l

The sensor base 30 is supported 'at the rear of coupler 28 within shell or casing 32, and comprises a commutator plate 34 hearing annular commutator rings forming part of the sensor.

Torque is supplied to shaft 12 by electric motor 40 mounted on base coupler 42 at the rear end of shell 32. Throughout the apparatus, securement'is obtained by suitable means such as set screws 44 and conventional threaded couplings as shown. Shaft 12 and the shaft of motor 40 are joined by drive coupling 46. Sleeve 48 is secured at 49 to shaft 12 within shell 32. Sleeve 48 carries on its forward end, spring arms 36 which bear on the rings of commutator plate 34, and transmit signals to the sensor evidencing resistance to torque supplied by the probe 10 as motor 40 is activated. Collar 13 on shaft 12 has leads 15 in circuit with spring arms 36. The sensor head is carried by the reaction head 20. The latter is fixedly engaged in earth at the remote end of bore hole 108. Thus, with rotative force being applied to the probe 10 in situ, shear strength data is derived in close proximity to an integral base in the earth.

Casing or shell 60 extends rearward of coupling 42, encases motor 40, and is coupled to pawl body 62 as shown in FIG. 5. Body 62 is transversely ported to provide slot 64. The longitudinally extending screw shaft 66 is journalled in slot 64 at its rear, by drive coupler 68, is secured to the shaft of reversible motor 70, which is mounted on block 72 secured within the next section of shell or casing 74. Operation of motor rotates screw 66 in one or the other direction.

Internally threaded traveller 76 is mounted on screw 66 and has outstanding arms 78. Opposed pawls or lugs 80,80 are mounted in slot 64 on pivot pins 82. A link 84 joins each lug to an arm 78 on traveller78. Movement of traveller 78, upon rotation of screw. 66, produces extension and retraction of pawlsv or lugs 80 depending upon the direction of motor rotation. When traveller-76 has fully extended the pawls, its rear bears on body 62 at the end of slot 64, and prevents further rotation of motor 70. This causes a rise in amperage which may be sensed by the operator'as an indication that the pawls are fully extended. Conversely, when traveller 76 is moved to the other end of slot 64, a

similar amperage rise will indicate full retraction of pawls 80.

Coupling 90 engages the rear of shell 74 and joins with shell section 92 which has access ports 94,96 near its ends. Shell 92 is provided with a knob 98 useful in pulling the probe and reaction equipment free from the earth following use, and preventing the equipment from dropping out of tube 100.

The drilling tube 100 has annular cutters 102 at its end, and includes an internal shoulder 104 which engages knob 98 during extraction of the probe. Once the probe is pulled free of the earth, it is hoisted to the surface by a cable 106 attached to terminal block 107.

When it is required to force the vaned probe 10 and reaction head 20 into the earth, the drill rod 100 is partially withdrawn from the remote end of bore hole 108. The probe is lowered through the casing 100 and, conditions permitting, it is dropped so that probe 10 and reaction 20 enter the earth. When greater force is required, which is usual, the pawls 80 are extended to the sides in advance of the operating end of the withdrawn drill casing 100. The casing is then lowered asv in FIG. 5. When the pawls 80 are contacted, the entire weight of the drilling casing bears on the instru-- ment and can be employed to force the leading end of the probe into the earth.

A very practical application of this invention occurs in connection with underwater drilling operations. in such an operation, working from a surface platform or a vessel, a drill casing is lowered to the bottom and the drilling commenced. It is desireable to periodically test the shear strength of the earth through which the drill casing is being driven, but without removal of the drill from the hole as to do so creates a tremendous problem of ever re-inserting the drill in the hole due to the effects of currents, tides, and the like.

The test equipment is designed to be inserted into the drill casing and by it guided to the end of the bore hole. When testing is desired, the drill is stopped and par tially withdrawn to retract the cutting end from the face of the bore hole 108. The casing of the test equipment passes down in the drill casing and partially extends through the cutting end 102 so that the probe 10 and reaction 20 contact the bore hole face. Ordinarily mere dropping of the test equipment package is incapable of driving the vaned probe 10 into the earth or of engaging the firmed reaction 20 therein. The operator then, having established contact with the bore hole face, activates motor 70 to rotate screw 66 thus causing pawls 80,80 outward beyond body 62 as shown in FIGS. 4 and 5.

Drill rod 100 is then lowered in the hole until the cutting end- 102 bears upon pawls 80,80 (see FIG. 5). Thus the entire massive weight of the lengthy drill casing 100 is transferred to the instrument package and hence to the probe and reaction 20.

The vanes 14 of the probe first slice into the earth at the face of bore hole 108 with minimal disturbance of the soil. Then the following vaned reaction enters the soil outward of the probe and forms an anchor or base for the instrument package proximate the probe, but without materially effecting the soil conditions at the probe.

When the operator is satisfied that the probe and reaction are properly placed, he energizes motor 40 applying torque to shaft 12. Sleeve 48 also tends to rotate with shaft 12 and to carry fingers 36 in rotation relative the annular rings of commutator disc 34 which are immovable. Variations in current flow occur and are detected in sensor 30 and transmitted via conventional conductors to the surface. It will be understood that all conductors for motors 40 and 70, and from sensor 30 are snaked lengthwise of the instrument package in passages provided (but not shown) in the various coupling and casing members. They all terminate in block 102 and thence pass to the surface as part of cable 106.

When readings have been taken and it is desired to resume drilling, the instrument package is to be withdrawn. Drill rod 100 is withdrawn from pawls they are then retracted into slot 64 in body 62. Then the drill casing is raised so that the internal lip or ledge 104 engages knob 98. Continued lifting of rod by the usually powerful system provided for such purposes applies longitudinal force on reaction 20 and probe 10 to withdraw it from the earth. Thereafter, the instrument package may be raised to the surface by its own cable 106 and drilling resumed. w

The various joints between couplings and casing sections of the instrument package are normally sealed and water tight to exclude moisture from the sensor andthe motors. The interior of the instrument package may also be pressurized before lowering by inserting air or an inert gas through fitting 110 on the side of coupling 90. Such internal pressurizing will serve to prevent water intrusion when the instrument is used at considerable depths where high fluid pressures may be encountered.

Although a particular and preferred embodiment of the apparatus is shown and described, modifications and alterations following a study of this disclosure will naturally become apparent to those skilled in the pertinent art. All such as fall within the spirit and scope of the following claims, giving due regard to the doctrine of equivalency, are intended to be covered by this patent.

What is claimed is:

1. Apparatus for in situ measurement of the torsional shear strength of earth located in advance of the remote end of a bore hole comprising:

a torsion shaft having a vaned end axially insertable into earth in advance of the remote end of a bore hole, said shaft terminating a nominal distance outward from the end of the bore hole;

torque-generating means associated with said shaft to urge rotation thereof;

anchor means including radial vanes engageable with the earth at the remote end of said bore hole, said anchor means surrounding said shaft between its vaned end and said torque-generating means;

rigid structure fixedly coupling said anchor means and said torque-generating means;

means located between said torsion shaft vaned end and said torque-generating means for sensing resistance to rotation of said shaft to torque applied thereto by said torque-generating means, said means for sensing resistance being operative to produce an electrical signal proportionate to the degree of resistive forced sensed;

means for transmitting said signal to external of the bore hole;

means for measuring the strength of such signal;

weight thereof to said rigid structure.

2. Apparatus according to claim 1 in which the rigid structure comprises a casing connecting between said torque-generating means and said anchor means.

3. Apparatus according to claim 1 in which the torque-generating means comprises a motor. 

1. Apparatus for in situ measurement of the torsional shear strength of earth located in advance of the remote end of a bore hole comprising: a torsion shaft having a vaned end axially insertable into earth in advance of the remote end of a bore hole, said shaft terminating a nominal distance outward from the end of the bore hole; torque-generating means associated with said shaft to urge rotation thereof; anchor means including radial vanes engageable with the earth at the remote end of said bore hole, said anchor means surrounding said shaft between its vaned end and said torque-generating means; rigid structure fixedly coupling said anchor means and said torque-generating means; means located between said torsion shaft vaned end and said torque-generating means for sensing resistance to rotation of said shaft to torque applied thereto by said torque-generating means, said means for sensing resistance being operative to produce an electrical signal proportionate to the degree of resistive forced sensed; means for transmitting said signal to external of the bore hole; means for measuring the strength of such signal; gravity actuated means operable to insert said vaned shaft and said anchor means into and to engage earth at the remote end of a bore hole; and said gravity-actuated means comprising expandible-retractible members associated with said rigid structure, and said bore is provided with a liner to engage said members when extended to apply the weight thereof to said rigid structure.
 2. Apparatus according to claim 1 in which the rigid structure comprises a casing connecting between said torque-generating means and said anchor means.
 3. Apparatus according to claim 1 in which the torque-generating means comprises a motor. 